New catalyst for safe, reversible hydrogen storage

Mar 18, 2012

This diagram shows the new catalyst in its protonated and deprotonated states as it reversibly converts hydrogen and CO2 gas to and from liquid formate or formic acid at ambient temperature and pressure. The gases can thereby be stored and transported as a liquid, and used later in carbon-neutral energy applications, simply by adjusting the pH.

(PhysOrg.com) -- Scientists at the Brookhaven National Laboratory and collaborators have developed a new catalyst that reversibly converts hydrogen gas and carbon dioxide to a liquid under very mild conditions. The work -- described in a paper published online March 18, 2012, in Nature Chemistry -- could lead to efficient ways to safely store and transport hydrogen for use as an alternative fuel.

Hydrogen is seen as an attractive fuel because it can efficiently be converted to energy without producing toxic products or greenhouse gases. However, the storage and transportation of hydrogen remain more problematic than for liquid hydrocarbon fuels. The new work builds on earlier efforts to combine hydrogen with carbon dioxide to produce a liquid formic acid solution that can be transported using the same kind of infrastructure used to transport gasoline and oil.

This is not the first catalyst capable of carrying out this reaction, but it is the first to work at room temperature, in an aqueous (water) solution, under atmospheric pressure  and that is capable of running the reaction in forward or reverse directions depending on the acidity of the solution, said Brookhaven chemist Etsuko Fujita, who oversaw Brookhavens contributions to this research.

When the release of hydrogen is desired for use in fuel cells or other applications, one can simply flip the pH switch on the catalyst to run the reaction in reverse, said Brookhaven chemist James Muckerman, a co-author on the study. He noted that the liquid formic acid might also be used directly in a formic-acid fuel cell.

Collaborator Yuichiro Himeda of the National Institute of Advanced Industrial Science and Technology (AIST) of Japan had been making substantial progress toward the goal of developing this type of catalyst for a number of years. He used iridium metal complexes containing aromatic diimine ligands (groups of atoms bound to the metal) with pendent, peripheral hydroxyl (OH) groups that can serve as acidic sites that release protons to become pendent bases.

Himeda recently entered into collaboration  via the U.S.-Japan Collaboration on Clean Energy Technology program  with Fujita, Muckerman, and Jonathan Hull (a Goldhaber Fellow working on Fujitas team). The Brookhaven group carried out coordinated experimental and theoretical studies to understand the sequence of chemical steps by which these catalysts converted H2 and CO2 into formic acid. Their goal was to design new catalysts with improved performance.

The Brookhaven teams key idea came from Nature: We were inspired by the way hydrogen bonds and bases relay protons in the active sites of some enzymes, Hull said.

Good catalysts efficiently move protons and electrons around, taking them from some molecules and placing them onto others to produce the desired product, he explained. Nature has many ways of doing this. Under the right conditions, the hydroxyl groups on the diimine ligand of the catalyst help hydrogen react with carbon dioxide, which is difficult to do. We thought we could improve the reactivity by placing the pendent bases near the metal centers, rather than in peripheral positions.

Once the Brookhaven team understood how Himedas catalysts worked, Hull realized that a novel ligand that had been synthesized by collaborators Brian Hashiguchi and Roy Periana of The Scripps Research Institute for an entirely different purpose would possibly be ideal for accomplishing this goal. The Brookhaven group designed a new iridium metal catalyst incorporating this new ligand.

Collaborator David Szalda of Baruch College (City University of New York) determined the atomic level crystal structure of the new catalyst to see how the arrangement of its atoms might explain its function.

Tests of the new catalyst revealed superior catalytic performance for storing and releasing H2 under very mild reaction conditions. For the reaction combining CO2 with H2, the scientists observed high turnovers at room temperature and ambient pressure; for the catalytic decomposition of formic acid to release hydrogen, the catalytic rate was faster than any previous report.

We were able to convert a 1:1 mixture of H2 and CO2 to formate (the deprotonated form of formic acid) at room temperature, successfully regenerate H2, and then repeat the cycle. Its a design principle we are very fortunate to have found, said Hull.

The regenerated high-pressure gas mixture (hydrogen and carbon dioxide) is quite pure; importantly, no carbon monoxide (CO)  an impurity that can poison fuel cells and thus reduce their lifetime  was detected. Therefore, this method of storing and regenerating hydrogen might have a use in hydrogen fuel cells.

Further efforts to optimize the hydrogen storage process are ongoing using several catalysts with the same design principle.

This is a wonderful example of how fundamental research can lead to the understanding and control of factors that contribute to the solution of technologically important problems, Muckerman concluded.

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What worse, the iridium is one of the most rarest and expensive elements at all, three times more expensive than platinum. http://static.saf...27_a.gif Such research isn't worth of consideration from practical perspective - it just serves as a salary generator of scientists involved.

What worse, the iridium is one of the most rarest and expensive elements at all, three times more expensive than platinum. http://static.saf...27_a.gif Such research isn't worth of consideration from practical perspective - it just serves as a salary generator of scientists involved.

catalyst's are not consumed so their initial cost is not very important

catalyst's are not consumed so their initial cost is not very important

Not true, considering if it were to be marketed then there would be a large consumption of the good, regardless if it needs to be replaced or not. Then, as cars would age, people would trash the cars and inevitably demand would also increase for the iridium... to what extent, who knows.

You didn't read the article properly: not good. They use *existing* CO2, reversibly, to store hydrogen.================

Callippo:

Such research isn't worth of consideration from practical perspective - it just serves as a salary generator of scientists involved.

Since you despise the endeavors of scientists so much, why don't you just stop using their results -- such as your computer. Log off and don't come back, if you seriously think that [some distressingly large percentage of] scientists are only in it for the money. (They are in it *partly* for the money, obviously -- they need to eat, just like you and me.)

As they said, the process is reversible, so no CO2 is generated. The easiest way to run it as carbon-neutral would be to collect the CO2 from the air, which industrial gas producers do every day, combine the H2, then, at the other end, return the CO2 to the atmosphere. Since CO2 is shipped around the country every day, it may even be possible to to use some of it at the other end, meaning that everything in the pipeline would be economically valuable.

My question is, what is the energy density? If the formate holds enough hydrogen per gallon it could be the solution to hydrogen fueled vehicles. After all, the main byproducts of today's cars are CO2 and water, and this would produce those without the noxious trace chemicals.

Don't know about energy density, but the weight of HCO2H is about 46 g/mole, and H2 is 2g/mole, so the hydrogen is about 4.34% of the total weight of just the formic acid, then the catalyst using just about the most dense metal known would greatly increase the weight. Which might not matter for a fixed storage system but for something like a car not so good.

How much catalyst would be needed to provide enough H2 for an average car?

We should ask about cost. Current price of hydrogen is about $4.00/kg, now the question about price of iridium required for its production. Annual production of iridium was around 3 tonnes, which defines it's usability for hydrogen economy.

I always find it funny that Armchair "scientists" always talk with absolutes, and true scientists always talk in grays, maybes and percentages of possibilities (yes there are established laws but even those real scientists hold out for something they may have missed or some other complexity)So, take this subject. . I see allot of it cant work, OMG CO2, and it is too much $$ . . Now I am sure the people that are commenting on this so vehemently have a grand and strangely convenient knowledge of the subject in great detail and all of the complexities to make such bold statments? ? If not . . start using qualifiers! to express a simple laymans option with the humility of probably being wrong but wanting to learn more. (insted of the standard insufferable clueless know it alls declarations of how it must be ) :P

It is obvious they know about the rarity of iridium. The last paragraph talks about formulating other catalysts, pretty clear they know the limitations of the present round of research. People should read the whole article before making these grand pronouncements like they are some kind of expert.

The obvious problem is, that it costs a lot of energy to collect CO2 out of the atmosphere to make it carbon neutral. Adding that cost to the hydrogen infrastructure wouldn't solve the storage and transportation problem - it would make it worse.

The gas would have to be recycled directly, but then you have a huge logistics problem on your hand, unless the system is stationary and can store and re-use the CO2 on-site.

Clearly this isn't a solution for portable applications, unless you're willing to waste most of the input energy.

How much catalyst would be needed to provide enough H2 for an average car?

We should ask about cost. Current price of hydrogen is about $4.00/kg, now the question about price of iridium required for its production. Annual production of iridium was around 3 tonnes, which defines it's usability for hydrogen economy.

I assume that the iridium is not a problem for production of it, but I assume that you also need a certain amount of this catalyst in the car to get the H2 out of it.

... or the fact that some cars have iridium in them already. (high end sparkplugs - so not that rare that they will not use it in a "throw away" part) and that we do not know the amount needed for the catalyst structure per unit that would be effective in say a car?!. That they may be a substitute (this just happens to be the first/best custom made catalyst for this process), Or that if we ever start harvesting meteors or asteroids iridium is rather abundant there. . Also it does not state that the CO2 used in the process needs to be Pure CO2 or what other gasses may poison this catalyst.So, what basis of all of this isn't a solution people are yammering about again? There is not enough information here to make a bold stamen like that. Try something like there could be a problem with availability or price of the catalyst or depending on the CO2 needs there could be additional energy costs

CO2 doesn't need to be collected from the air, we have abundant amounts of CO2 available from our fossil fuel electrical plants, and will for many decades to come.The question I have is where the hydrogen is going to come from.As far as I know it is still less than 50% efficient to split H2O.Also the fuel cell are typically less than 50% efficient.So we are now down to less tahn 25%, then we lose another 10% in the electric car motors and controllers and our efficiency is down to less than 20%.

@Erog-- Regular readers of Physorg see dozens of articles per year about scientists who are using catalysts to try to solve big Energy and Environmental problems. Some of these scientists are using impossibly rare and expensive catalysts, while others try it the hard way with common and affordable catalysts. Most of us regulars have learned to quickly spot the realists.

This article buries the chemical name of the catalyst deep in the text, and does not give any indication that Iridium is rare and costs thousands of dollars per ounce. Instead, the p.r. announces: "This is a wonderful example of how fundamental research can lead to the understanding and control of factors that contribute to the solution of technologically important problems."

The BS isn't hard to spot. If these guys can come back with a more realistic catalyst, they will get a better reception on this forum.

The efficiency sounds about right, but a typical gasoline engine and transmission is also 20% to 25% efficient, so that seems to be a draw.

It depends on the energy source. If you have to make the energy by burning something, then it's very much a non-starter. You stand to lose up to 75% of the primary energy source just by getting the hydrogen to the fuel tank.

But if you can get electricity directly out of a device like a solar panel or a windmill, you can get about 40% of the energy back, assuming that you lose neglible amount in storing and transporting it.

However, there's an additional cost to making hydrogen, because it requires purified clean water. Otherwise the electrolysis cells will get polluted by the minerals that it carries because they get concentrated in the cells. That's why there isn't a large scale water splitting plant in operation to date - practically all hydrogen on the market is made by reforming natural gas.

In the absence of fossil fuels, especially natural gas, all the hydrogen we can produce would go towards making plastics, feedstock for chemical processes, and fertilizers in particular.

Without cheap hydrogen from natural gas, chemicals like ammonia and potassium nitrate would get very expensive very fast, because they are essential for maintaining our current level of food production.

Hydrogen will be more valuable as an industrial chemical rather than an energy carrier.

Of course, this research is an apparent nonsense from practical perspective - but it still doesn't explain, why first comment pointing in this direction got -15 points. Some people apparently love being a trolls (voters were for example: Sanescience, gopher65, Parsec, jonnyboy, gwrede, ghidon, Erog, kaasinees, Ojorf, jibbles, Scottingham, encoded, CardacianNeverid | Pluton, atomsk).

You stand to lose up to 75% of the primary energy source just by getting the hydrogen to the fuel tank.

We discussed it in wider extent here http://www.physor...ife.html Essentially, every research in this direction is harmless, because it just delays and betrays the money from the research of the only one perspective energy source: the cold fusion. It's not just about money wasted in hydrogen economy, the actual cost of this useless research is way higher.

"practically all hydrogen on the market is made by reforming natural gas." That leaves the carbon, which could be burned to make energy to run the process, resulting in CO2, which in turn could be fed into the catalyst system with the hydrogen. Not carbon neutral, but it uses the entire methane molecule.

There are reasons why this is not practical as a CO2 neutral process. For one there is no way you make it economical or viable if you are using the CO2 from the air. It would require far too much energy to separate the 300-400ppm CO2 in the air to a concentration high enough to make this process reasonable. The second reason why its not CO2 neutral is it would rely on tag teaming with a CO2 generator such as coal power to produce a decent stream of CO2 to use, and therefore rules out non CO2 generating process of wind, solar, nuclear, cold fusion, dilithium chambers.

It is practical if the storage tank is stationary, because then you can just keep recycling the same CO2.

The problem of large scale hydrogen storage is, that to have it in any reasonable volume, you have to turn it into a liquid, and cooling it down to temperature where it stays that way uses massive amounts of energy, continuously, because you have to keep pumping heat out or it'll just boil off.

Turning it into a chemical that is stable at room temperature saves you a lot. It means you can actually stockpile hydrogen.

It's basic research. They aren't developing a product, they're figuring out how chemistry proceeds. There's no need to throw stones or complain that they haven't worked out practical commercial applications.

It's far too early to say that hydrogen will become commercially useful in vehicles. But even if that never pans out, catalysis has many other potential uses. It's a good thing to research.

Eikka, so instead of storing H2 now you have to store the same volume of CO2? This whole method only benefits you if you are using H2 like we do gasoline now, fill and go. In that case once you are at the end of a "tank" then you have to store all the CO2 you generated, which has some of the same fundamental issues you stated H2 does, compressors, high pressure tanks, etc. Its also not feasible that the CO2 from the air is what is used because the concentration is so low. Even if you can over come the highly suppressed reaction rate, you would have to have an air blower the size of 4 of your cars to bubble enough air through the solution. The chemistry is cool and does make storage easier, but my original point was that the system is NOT CO2 neutral, and I think that those driving the funds are going to see that as a no go as jittery as they are about global warming etc. Your stockpile of H2 is a 1:1 release of CO2.

For example results of industrial nitric acid production show, that the rate of platinum loss from platinum-rhodium alloy used is 0.044 gram platinum per ton nitric acid at atmospheric pressure and 0.121 gram platinum per ton nitric acid at medium pressure. And this is a heterogenous gas catalysis, where the consumption of rare metal is extraordinarily low. At the case of iridium we are talking about homogeneous catalysis, where the consumption of catalyst is usually two-three orders higher...

The annual production of iridium are just three tons - try to estimate the amount of hydrogen, which we could produce with it and compare it with amount of gasoline consumed annually (~ 700 million gallons per day). The people should learn at least trivial algebra, before they start to judge some technology.

Very true, and possibly a relatively inexpensive way to store power from wind, solar, tides, etc. Everything would stay at the generating site, including the CO2, and it would be used as fuel for a thermal generating plant. When there is excess electricity, you split the water and store the H2. When you need extra electricity, run the H2 through a gas turbine, as in the natural gas "on demand" plants. Capture the CO2, and condense the water from the turbine if needed, or use fresh water if available, and restock the fuel tank when power is available. Basically an alternative to batteries.

I wonder if this would work for rocket fuel? Not for takeoff, but for orbit to orbit use. Carry the formate and oxidizer, split the formate, burn the hydrogen, and and heat the CO2. Instead of using only the fuel and oxidizer as reaction mass, you'd also use the stabilizer. You'd get less thrust per pound of fuel, but have a lot more pounds, and wouldn't have to keep the H2 cold.

what part of just because its in writing doesn't make it true don't you understand? There is no cost effective way to get the high concentration of CO2 needed for this reaction without creating it specifically for the reaction. Seeing as that would later result in CO2 let out in to the atmosphere as the H2 is used, that hardly screams neutral. Next time, think farther down the road than "they said it was so."

Pulling CO2 out of the air at STP (atmospheric pressure at 20 degrees C) is quite easy. Nuclear submarines do it all the time. In this case a membrane type system should work fine.

As for the Iridium argument calm down already. Lots of catalysts for decomposing formate into CO2 and H2 are known. The Iridium catalyst works for making formate. (The fact that it can also be used at different pH to decompose formate is interesting, but only to theorists. ;-)

Can any catalyst "lost" during the formation process be trapped and recycled? Sure. In fact, with properly shaped storage tanks, you probably tap off the bottom gallon or three, and process them to recover the catalyst. It is much, much heavier than formate.

Oil is the only reason for the persistence of the US empire. The only thread holding the USA together is the petrodollar. Alternate technologies cannot dominate until the US empire is decimated by it's collapsing bond market and subsequent economic implosion. This will begin in July when Iran sells oil directly in ALL major currencies, not only the US dollar. Unless, of course, the USA police state chooses to annex Iran as it has other nations (Iraq, Libya) threatening to sell oil in euros. US has no interest in Syria which has no oil. With the decline of the USA empire alternate energy technologies will finally thrive.

If you are keeping the storage tank stationary what is the benefit of a transportable liquid? In addition, what are you going to do with all the CO2 that comes off the reaction. You get the same CO2 as H2 out of the reaction so you are going to use a decent amount of H2 then you have to store the CO2 which takes a relatively high amount of energy as in the liquid H2.

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